Don't worry too much about your neck bolt if things are tight and play well. But to repair it permanently, you will have to remove the neck and drill out the offending hole with a bit that is slightly larger than the hole itself. Be careful not to go drill deeper than the existing hole. Then get a hardwood dowel to fit, even a basswood dowel will work though I like to use maple if it's available. Remember this will only be about 1/8" thick so it's more of a small stick than a dowel. Make sure that the dowel fits, but not too tight. It helps also if you'll carve a groove in the dowel for the glue to squeeze through. For simplicity use carpenters glue and fill the hole then tap the dowel in. After the glue dries, trim the dowel flush with the surface of the neck heel and do a fit-up with the body and redrill the hole to fit your screw. Then just reassemble and voila, good as new!!

I use a plug cutter to make the dowel. A ready made dowel has the grain running along the length. By cutting the plug out of the face of a piece of stock, the grain runs in a direction that provides cross grain for the screw threads. Tear out is much less of a problem when threaded cross grain.

Another problem with dowels is incosistency in the diameters. The dowels that are available at the DIY stores are often off as much as 1/32".

For actual doweling purposes I make my own. I have a piece of 3"channel iron with holes drilled through it that corr- esponds with the dowel diameter. If I need a 1/4" dowel I rough out a blank around 5/16" and just drive it through the 1/4" hole. They come through the hole perfectly round exactly the size of the hole.

I realize that the last paragraph has nothing to do with the original question but I thought that you, as a woodworker, might find it of interest.

The glue groove that you pointed out is excellent advice. If the plug fits as it should there is very little space left for the glue.

oooh, I like the die method of sizing your dowels. I'll have one of those in just a few minutes. Thanx for sharing.

I had to make dowels for filling some pickguard holes. I started with a 1/8" dowel, then chucked it in the drill press, turned it on, and sanded it to a perfect taper for insertion. Worked like a charm.